1. Field of the Invention
Exemplary embodiments of the present invention relate to a device for a solid oxide fuel cell or a solid oxide electrolysis cell, the device comprising an integral one-piece construction including a current collector and a manifold.
2. Description of Related Art
A solid oxide fuel cell is a system that generates electricity by the reaction of fuel (hydrocarbon or hydrogen) with oxygen in the air at a high temperature of 500 to 1,000° C. Similarly, a solid oxide electrolysis cell is a system that electrolyzes steam into hydrogen and oxygen at a high temperature of 500 to 1,000° C.
Such solid-oxide fuel cells or solid oxide electrolysis cells are generally classified by shape into a planar type, a tubular type and a flat tubular type.
The planar solid oxide fuel cell, or electrolysis cell, has the advantage of a high power density (output power). However, the planar solid oxide fuel cell or electrolysis cell has disadvantages in that the area containing the gas seal is relatively large, thermal shock (thermal stress) occurs due to the difference in the coefficient of thermal expansion between materials during stacking and it is difficult to achieve a large electrode area.
The tubular fuel cell has advantages in that it has a relatively high thermal stress resistance and mechanical strength, can be manufactured by extrusion molding and makes it possible to achieve a large electrode area. However, the tubular fuel cell has the limitation of low power density.
The flat tubular fuel cell combines the advantages of the planar and tubular fuel cells (electrolysis cells).
The flat tubular fuel cell is advantageous over the tubular fuel cell in that it has a relatively high power density (output power), thermal stress resistance and mechanical strength.
In spite of such advantages, the tubular solid oxide fuel cell and electrolysis cell has a disadvantage in that it requires an excessively large number of stack components, including a unit cell, a connection material, a current collector, a manifold, a housing, an insulation material and a sealing material.
Particularly, the current collector serves to collect electricity generated in a stack of unit cells at high temperature or to supply the electricity, and the manifold is an important component through which gas is supplied to the fuel stack or discharged therefrom. The two components are generally connected with each other.
In conventional tubular or flat tubular solid oxide fuel cells and electrolysis cells, a metallic current collector is generally used to collect electricity generated in the cell stack, and the manifold for supplying gas to the cell stack is provided as a component separate from the current collector.
In this case, a brazing or thermal bonding process for joining the manifold with the current collector is carried out, thus increasing the process time and the manufacturing cost.
In addition, in the case of conventional tubular or flat tubular solid oxide fuel cells and electrolysis cells, a cell stack provided with the current collector separately from the manifold should be manufactured, and thus the total volume of the cell is increased.
Furthermore, in the case of conventional tubular or flat tubular solid oxide fuel cells and electrolysis cells, a brazing process or a bonding process of joining the current collector with the manifold is carried out. In this process, stress can occur in the cell due to the difference in the coefficient of thermal expansion between materials, and thus the cell can be damaged or gas can leak from the cell during operation.
Specifically, in the case of most of tubular or flat tubular fuel cells, a process of sealing with glass ceramic or a brazing process employing a metal filler is carried out to join a metal cap with a ceramic tube in order to seal the gas.
However, in case the cell is sealed with glass ceramic, there is a problem in that the cell or the glass seal is broken down due to the difference in the coefficient of thermal expansion therebetween.
In addition, when the metal cap and the ceramic tube are brazed using the metal filler, the difference in the coefficient of thermal expansion can be minimized, but the filler metal can be corroded and reduced during the brazing process, thus causing a problem in terms of the long-term stability of the cell. In addition, the filler metal has a low melting point, the operation of the cell at high temperature (850° C. or higher) is limited. Moreover, because the reducibility of the brazing process is very low, the process has a very low yield and is very expensive.
Accordingly, the present inventors have conducted studies to solve the above-described problems and, as a result, have developed a device for a solid oxide fuel cell or a solid oxide electrolysis cell, the device comprising an integral one-piece unit including a current collector and a manifold, which corresponds to an aspect of the present invention.